Re: [PATCH 2/3] KVM: nVMX: Fix fail to get nested ack intr's vector during nested vmexit

Paolo Bonzini
2014-07-17T09:46:37Z

Il 17/07/2014 06:56, Wanpeng Li ha scritto:
> && nested_exit_intr_ack_set(vcpu)) {
> int irq = kvm_cpu_get_interrupt(vcpu);
> +
> + if (irq < 0 && kvm_apic_vid_enabled(vcpu->kvm))
> + irq = kvm_get_apic_interrupt(vcpu);

There's something weird in this patch. If you "inline"
kvm_cpu_get_interrupt, what you get is this:

int irq;

/* Beginning of kvm_cpu_get_interrupt... */
if (!irqchip_in_kernel(v->kvm))
irq = v->arch.interrupt.nr;
else {
irq = kvm_cpu_get_extint(v); /* PIC */
if (!kvm_apic_vid_enabled(v->kvm) && irq == -1)
irq = kvm_get_apic_interrupt(v); /* APIC */
}

/* kvm_cpu_get_interrupt done. */
if (irq < 0 && kvm_apic_vid_enabled(vcpu->kvm))
irq = kvm_get_apic_interrupt(vcpu);

There are just two callers of kvm_cpu_get_interrupt, and the other is
protected by kvm_cpu_has_injectable_intr so it won't be executed if
virtual interrupt delivery is enabled. So you patch is effectively the
same as this:

diff --git a/arch/x86/kvm/irq.c b/arch/x86/kvm/irq.c
index bd0da43..a1ec6a5 100644
--- a/arch/x86/kvm/irq.c
+++ b/arch/x86/kvm/irq.c
@@ -108,7 +108,7 @@ int kvm_cpu_get_interrupt(struct kvm_vcpu *v)

vector = kvm_cpu_get_extint(v);

- if (kvm_apic_vid_enabled(v->kvm) || vector != -1)
+ if (vector != -1)
return vector; /* PIC */

return kvm_get_apic_interrupt(v); /* APIC */

But in kvm_get_apic_interrupt I have just added this comment:

/* Note that we never get here with APIC virtualization
* enabled. */

because kvm_get_apic_interrupt calls apic_set_isr, and apic_set_isr must
never be called with APIC virtualization enabled either. With APIC
virtualization enabled, isr_count is always 1, and highest_isr_cache is
always -1, and apic_set_isr breaks both of these invariants.

Paolo